1. Field of the Invention
The present invention relates to an arrangement for controlling throttle valve opening for an internal combustion engine, and, in particular, to a control arrangement for an automobile engine having an actuator for opening and closing a throttle valve, a detector for detecting a controlled position of the throttle valve and a control unit which compares an output from the detector with a controlled target opening of the throttle valve, and feed-back controls for adjusting the opening of the throttle valve based on the comparison result, thereby controlling the opening of the throttle valve with a degree of high accuracy.
2. Description of Related Art
These days, in place of a conventional control arrangement for throttle valve opening wherein the throttle valve is directly operated by depression of an acceleration pedal, a control arrangement of throttle valve opening for an internal combustion engine used in a motor vehicle such as an automobile, a so called electronic throttle control arrangement of throttle opening has drawn attention in which a control input of the acceleration pedal is detected by a sensor in a form of electrical signal which is treated in accordance with a predetermined processing operation, and supplied to an actuator such as an electric motor that controls the opening of a throttle valve based on the processed electrical signal. The so called electronic throttle control arrangement of the throttle opening has been applied to many kinds of engine controls such as a traction control which is effective for enhancing performance of an automobile such as engine output enhancement.
Other than the above exemplified engine control, the so called electronic throttle control arrangement of the throttle opening can be applied for an idle speed control (ISC) and a fast idle control (FIC) in a region of a low throttle valve opening.
However, in a conventional ISC arrangement as, for example, disclosed in JP-B-63-49112(1988) which corresponds to U.S. Pat. No. 4,895,126, control of the idling rpm of an engine of a motor vehicle to a predetermined level in accordance with the temperature of water or an electric load has been effected by providing a bypass passageway to a throttle chamber for bypassing the throttle valve so as to regulate the volume of air flowing through the bypass passageway by ulilizing the pressure differential between the inlet and the outlet of the throttle valve.
Likely, in a conventional FIC arrangement, through a provision of an air regulator in a similar bypassing passageway, the volume of air flowing therethrough during a low temperature starting-up period is regulated.
In the conventional arrangements, auxiliary devices were indispensable for the ISC and FIC, and it was thus difficult to suppress the total leakage air amount. Therefore, when lowering of set idling rpm is required, it was necessary to modify the fundamental structure of the arrangements. Further, was difficult to reduce the manufacturing cost due to necessity of the auxiliary devices.
On the other hand, when control of a throttle valve in a region of low throttle valve opening is effected by the electronic throttle control arrangement, it was difficult to achieve a stable engine rpm during ISC and FIC engine controls because of an insufficient control accuracy of the arrangement due to a poor resolution of a throttle valve position sensor in a region of low throttle valve opening degrees.